1. Field of the Invention
The present invention generally relates to fluid coupling devices, and more particularly to a torsional vibration damper for hydrokinetic torque-coupling devices, and a method for making the same.
2. Background of the Invention
A conventional hydrokinetic torque-coupling device 1 is schematically and partially illustrated in FIG. 1 and is configured to transmit torque from an output shaft of an internal combustion engine in a motor vehicle, such as for instance a crankshaft 2a, to a transmission input shaft 2b. The conventional hydrokinetic torque-coupling device comprises a hydrokinetic torque converter 4 and a torsional vibration damper 5. The hydrokinetic torque converter conventionally comprises an impeller wheel 4i, a turbine wheel 4t, a stator (or reactor) 4s fixed to a casing of the torque converter 4, and a one-way clutch for restricting rotational direction of the stator 8 to one direction. The impeller wheel 4i is configured to hydro-kinetically drive the turbine wheel 4t through the reactor 4s. The impeller wheel 4i is coupled to the crankshaft 1 and the turbine wheel 4t is coupled to a guide washer 6.
The torsional vibration damper 5 of the compression spring-type comprises a first group of coil springs 7a, 7b mounted between the guide washer 6 and an output hub 8 coupled to the transmission input shaft 2b. The coil springs 7a, 7b of the first group are arranged in series through a phasing member 9, so that the coil springs 7a, 7b are deformed in phase with each other, with the phasing member 9 being movable relative to the guide washer 6 and relative to the output hub 8. A second group of coil springs 7c is mounted with some clearance between the guide washer 6 and the output hub 8 in parallel with the first group of elastic members 7a, 7b, with the coil springs 7c being adapted to be active in a limited angular range, more particularly at the end of the angular travel of the guide washer 6 relative to the output hub 8. The angular travel, or the angular shift noted α, of the guide washer 6 relative to the output hub 8, is defined relative to a rest position (α=0) wherein no torque is transmitted through damping means formed by the coil springs 7a, 7b. The second group of coil springs 7c makes it possible to increase the stiffness of the damping means at the end of angular travel, i.e. for a significant a angular offset of the guide washer 6 relative to the output hub 8 (or vice versa).
The torque-coupling device 1 further comprises a lock-up clutch 3 adapted to transmit torque from the crankshaft 2a to the guide washer 6 in a determined operation phase, without action from the impeller wheel 4i and the turbine wheel 4t. 
The turbine wheel 4t is integrally or operatively connected with the output hub 8 linked in rotation to a driven shaft, which is itself linked to an input shaft of a transmission of a vehicle. The casing of the torque converter 4 generally includes a front cover and an impeller shell which together define a fluid filled chamber. Impeller blades are fixed to an impeller shell within the fluid filled chamber to define the impeller assembly. The turbine wheel 4t and the stator 4s are also disposed within the chamber, with both the turbine wheel 4t and the stator 4s being relatively rotatable with respect to the front cover and the impeller wheel 4i. The turbine wheel 4t includes a turbine shell with a plurality of turbine blades fixed to one side of the turbine shell facing the impeller blades of the impeller wheel 4i. 
The turbine wheel 4t works together with the impeller wheel 4i, which is linked in rotation to the casing that is linked in rotation to a driving shaft driven by an internal combustion engine. The stator 4s is interposed axially between the turbine wheel 4t and the impeller wheel 4i, and is mounted so as to rotate on the driven shaft with the interposition of the one-way clutch.
While conventional hydrokinetic torque-coupling devices, including but not limited to those discussed above, have proven to be acceptable for vehicular driveline applications and conditions, improvements that may enhance their performance and cost are possible.